1. Field of the Invention
The present invention relates to a method of disposing an electronic device on an electrode formed on a substrate to connect electrically the electronic device and the electrode.
2. Description of Related Art
Active-type liquid crystal display devices and organic electroluminescence display devices, in which a plurality of pixels are arranged in a matrix, are formed on glass substrates. Each of these pixels is controlled by a transistor provided in the vicinity of the pixel.
With current technology, however, crystalline semiconductor transistors cannot be formed on a glass substrate. Therefore, thin film transistors for controlling pixels are formed using an amorphous silicon or polysilicon thin film. Such thin film transistors have the advantage that they can be fabricated on a large-area substrate at low cost, but have the disadvantage that their lower mobility than crystalline silicon prevents them from operating at high speed.
To overcome this disadvantage, the present inventor has proposed the following method of disposing transistors on a substrate. In this method, a large number of transistors are fabricated previously on a monocrystalline silicon wafer and then cut into individual pieces from the silicon wafer to be dispersed in a liquid.
Then, the liquid is spread on a substrate so that the transistors are disposed on the substrate (see U.S. patent application Ser. No. 12/088,194, particularly FIG. 34 and FIG. 36). This method makes it possible to form a high-performance transistors composed of crystalline silicon on a glass substrate.
The method described in U.S. patent application Ser. No. 12/088,194 are shown in FIGS. 8A and 8B, FIGS. 9A and 9B, FIGS. 10A to 10C, FIGS. 11A and 11B, and FIGS. 12A to 12D.
FIGS. 8A and 8B, FIGS. 9A and 9B, FIGS. 10A to 10C, and FIGS. 11A and 11B show in this order the steps of the method described in U.S. patent application Ser. No. 12/088,194. FIG. 8B is a cross-sectional view taken along a line I-I of FIG. 8A. FIG. 9B is a cross-sectional view taken along a line II-II of FIG. 9A. FIGS. 10B and 10C are cross-sectional views taken along a line III-III of FIG. 10A and show the time course of the same region, which changes from a state shown in FIG. 10B to a state shown in FIG. 10C with time. FIG. 11B is a cross-sectional view taken along a line IV-IV of FIG. 11A.
FIG. 12A is a schematic diagram of a transistor 810 to be disposed. FIG. 12B is a schematic diagram of the back side of the transistor 810 shown in FIG. 12A. FIG. 12C is a detailed schematic diagram of a hydrophilic region 802 to be formed on a substrate. FIG. 12D is a schematic diagram showing a state in which the transistor 810 is disposed in the hydrophilic region 802.
As shown in FIGS. 8A and 8B, first, a plurality of hydrophilic regions 802 surrounded by a water-repellent region 803 are formed in a matrix on the surface of a substrate 801. To form the water-repellent region 803, a target region is modified chemically with a silane coupling agent containing fluorocarbon chains, such as CF3(CF2)7C2H4SiCl3, or a silane coupling agent containing hydrocarbon chains, such as CH3(CH2)17SiCl3, so as to be rendered water-repellent. According to the description of U.S. patent application Ser. No. 12/088,194, a person skilled in the art can modify chemically only a target region with a silane coupling agent to render the region water-repellent.
As shown in FIG. 12C, a first electrode 906, a second electrode 907, and a third electrode 908 are formed in and around the hydrophilic region 802. A part of the first electrode 906 is formed in the hydrophilic region 802 and has a hydrophilic surface. This part is referred to as a hydrophilic first electrode 906b. The other part of the first electrode 906 is formed outside the hydrophilic region 802 and has a water-repellent surface. This part is referred to as a water-repellent first electrode 906a. Likewise, the second electrode 907 is composed of a water-repellent second electrode 907a and a hydrophilic second electrode 907b, and the third electrode 908 is composed of a water-repellent third electrode 908a and a hydrophilic third electrode 908b. 
A hydrophilic metal or a hydrophilic substrate can be used to form the hydrophilic region 802. Examples of the hydrophilic metal include nickel, aluminum, and copper. Examples of the hydrophilic substrate include a glass substrate, a silicon substrate having an oxide film formed on its surface, and a nylon resin substrate. A metal or a substrate also may be exposed to oxygen plasma or ozone to render the surface thereof hydrophilic.
Next, as shown in FIGS. 9A and 9B, a first squeegee 804 is moved in the direction of an arrow 807 relative to the substrate 801 to apply water 805 onto the substrate 801. As a result, the water is disposed in the hydrophilic region 802. In these diagrams, the reference numeral 806 denotes the water that has been disposed in the hydrophilic region 802.
Then, as shown in FIGS. 10A to 10C, a second squeegee 808 is moved in the direction of an arrow 813 relative to the substrate 801 before the water 806 disposed in the hydrophilic region 802 volatilizes. Thus, a transistor-dispersed liquid 809 is applied to the substrate 801. In this transistor-dispersed liquid 809, a plurality of transistors 810 are dispersed in dichlorobutane 811.
The transistor 810 is described in detail below.
As shown in FIG. 12A, the transistor 810 is a rectangular parallelepiped. On one of the surfaces with the largest area, a gate electrode 902, a source electrode 903, and a drain electrode 904 are formed. The surface on which these electrodes 902 to 904 are formed is referred to as an electrode surface 901. Like ordinary transistors, the source electrode 903 and the drain electrode 904 have the same function. That is, the source electrode 903 may be used as a drain electrode. The drain electrode 904 may be used as a source electrode likewise.
The shape and size of the electrode surface 901 are the same as those of the hydrophilic region 802 shown in FIG. 12C. The shapes and sizes of the hydrophilic first electrode 906b, the hydrophilic second electrode 907b, and the hydrophilic third electrode 908b are the same as those of the gate electrode 902, the source electrode 903, and the drain electrode 904, respectively. Preferably, the material of these electrodes is palladium or nickel. An electrode having a multilayer structure with an outermost surface composed of palladium or nickel may also be used.
The surface of the transistor 810 is previously modified chemically with 1-chloroethyltrichlorosilane.
When this transistor-dispersed liquid 809 in which a plurality of such transistors 810 are dispersed in dichlorobutane 811 is applied onto the substrate 801, each of the transistors 810 moves from the dichlorobutane 811 to the water 806, as shown in FIGS. 10B and 10C. In FIG. 10C, the reference numeral 812 denotes the transistor that has moved into the water 806. The transistor 810 moves in this way because the water 806 and the dichlorobutane 811 have no compatibility with each other and the surface of the transistor 810 has been modified chemically with 1-chloroethyltrichlorosilane. Specifically, this chemical modification allows the transistor 810 to have higher wettability to the water 806 than that to the dichlorobutane 811. Accordingly, the transistor 810 moves from the dichlorobutane 811 with lower wettability to the water 806 with higher wettability. Since the water 806 and the dichlorobutane 811 have no compatibility with each other, even if the dichlorobutane 811 is applied onto the water 806, the water 806 stays there stably.
When the transistor 810 moves to the water 806, the following two cases are considered: the electrode surface 901 faces the hydrophilic region 802; and the surface 905 opposite to the electrode surface 901 faces the hydrophilic region 802. When the electrode surface 901 faces the hydrophilic region 802, the gate electrode 902, the source electrode 903, and the drain electrode 904 come into contact with the hydrophilic first electrode 906b, the hydrophilic second electrode 907b, and the hydrophilic third electrode 908b, respectively. In this way, the electrodes 902 to 904 of the transistor 810 are brought into physical contact respectively with the hydrophilic electrodes 906b to 908b formed on the substrate 801 to be connected electrically to the hydrophilic electrodes 906b to 908b. When the surface 905 opposite to the electrode surface 901 faces the hydrophilic region 802, a step of connecting the electrodes 902 to 904 of the transistor 810 respectively with the electrodes 906 to 908 formed on the substrate 801 is provided additionally.
Then, the water 806 is removed by volatilization. As a result, a transistor 814 is disposed in the hydrophilic region 802, as shown in FIGS. 11A and 11B. In these diagrams, the reference numeral 814 denotes the transistor that has been disposed in the hydrophilic region 802.